While the exact mechanisms of ischemia/reperfusion injury remain to be elucidated, inhibition of complement activation (e.g., sCR1 or C 1 esterase inhibitor), depletion of complement components (e.g., cobra venom factor) and complement component (e.g., C3 and C4) knockout mice have revealed an important role of complement in ischemia/reperfusion injury. During the previous two funding cycles we have shown that the complement component C5 plays an important role in the pathogenesis of reperfusion injury and in the production of vasoactive eicosanoids. These preclinical findings have led to two 1000 patient Phase II clinical trials in acute myocardial infarction. Further, we have shown that mannose binding lectin (MBL) may play an important role in the initiation of complement activation following ischemia/reperfusion (I/R). However, the specific pathways involved, the order of pathway activation, and the specific contribution of C5a versus C5b-9 in the setting of I/R is not well characterized. Reports in the literature suggest that the classical pathway is the initiating complement pathway involved in I/R injury by way of natural antibody deposition. Our preliminary data suggest that the lectin pathway is involved and may be the initiating pathway. This application will investigate the several "holes" present in our knowledge about complement and its role in mediating tissue injury and inflammation associated with myocardial (M) I/R. Novel anti-complement reagents and knockout mice have been developed and will be developed for characterizing the role of specific complement components in MI/R. Specifically we will identify the importance of each specific complement pathway (e.g., lectin, classical and alternative) in M I/R. Previous reports by our group and others have demonstrated that complement activation influences gene expression and we will identify novel pro- and anti-inflammatory genes that are regulated by C5a and/or C5b-9. The approach for this competitive renewal is to identify the specific role of C5a, C5b-9, C1q, MBL and factor D in MI/R. We will identify/characterize C5a or C5b-9 induced gene expression in vitro using isolated myocytes from rats and humans. Novel and potential therapeutically useful reagents will be made and used in vivo to establish and validate the genes expressed in vitro, anti-inflammatory effects and resolution of inflammation in vivo. Our aims are to: 1) Characterize complement pathways involved in complement activation on anoxic/reoxygenated myocytes; 2) Develop novel reagents against "key" complement components to investigate fully the role of complement in MI/R and 3) Characterize the role of specific complement pathways in MI/R in vivo.